Turbocharged and supercharged engines may be configured to compress ambient air entering the engine in order to increase power. Compression of the air may cause an increase in air temperature, thus, an intercooler or charge air cooler (CAC) may be utilized to cool the heated air thereby increasing its density and further increasing the potential power of the engine. Condensate may form in the CAC when the ambient air temperature decreases, or during humid or rainy weather conditions, where the intake air is cooled below the water dew point. Condensate may collect at the bottom of the CAC, or in the internal passages, and cooling turbulators. Under certain air flow conditions, condensate may exit the CAC and enter an intake manifold of the engine as water droplets. If too much condensate is ingested by the engine, engine misfire and/or combustion instability may occur.
Other attempts to address engine misfire due to condensate ingestion include avoiding condensate build-up. In one example, the cooling efficiency of the CAC may be decreased in order to reduce condensate formation. However, the inventors herein have recognized potential issues with such methods. Specifically, while some methods may reduce or slow condensate formation in the CAC, condensate may still build up over time. If this build-up cannot be stopped, ingestion of the condensate during acceleration may cause engine misfire. Additionally, in another example, engine actuators may be adjusted to increase combustion stability during condensate ingestion. In one example, the condensate ingestion may be based on a mass air flow rate and amount of condensate in the CAC; however, these parameters may not accurately reflect the amount of water in the charge air exiting the CAC and entering the intake manifold. As a result, engine misfire and/or unstable combustion may still occur.
In one example, the issues described above may be addressed by a method for adjusting engine actuators based on an amount of water in charge air exiting a charge air cooler, the amount of water based on an output of an oxygen sensor positioned downstream of the charge air cooler (CAC). Specifically, the oxygen sensor may be positioned at an outlet of the CAC. The oxygen sensor may be operated in either a variable voltage mode or a base mode based on exhaust gas recirculation (EGR) flow. For example, if EGR flow is greater than a threshold, the oxygen sensor may operate in the variable voltage mode to measure oxygen content of the charge air at the outlet of the CAC. The amount of water in the charge air exiting the CAC may then be determined based on a pumping current of the oxygen sensor. For example, a saturation water value at an outlet temperature condition of the CAC may be subtracted from the total water measured by the oxygen sensor to determine the amount of water in the form of droplets in the charge air. An engine controller may then adjust engine actuators to increase combustion stability in response to the amount of water in the charge air exiting the CAC. For example, the controller may adjust spark timing to increase combustion stability during the ingestion of the determined amount of water. In this way, engine misfire and combustion instability due to water ingestion may be decreased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.